RemoveHopByHopFilter removes the connection header, but doesn't remove the listed headers in it (as it should per e.g. https://www.rfc-editor.org/rfc/rfc9110.html#name-connection or https://datatracker.ietf.org/doc/html/rfc2616#section-14.10). For example, if the header was Connection: xyz then the xyz header would need to be removed as well.

Note that the test code in RemoveHopByHopHeadersFilterTests.removesHeadersListedInConnectionHeader passes because the chosen values of upgrade and keep-alive are listed explicitly in RemoveHopByHopFilter and not because they are in the Connection header value - this is fine since those two headers need to be removed anyway per the specs (whether they are listed in connection header or not).